So I really liked this game when it first came out. One of my friends got a 4-pack during the free weekend and we all played a few hours. 3 days later the community was dead and there was nobody on any of the servers. I've been thinking about why this happened.
First of all, the player has only 3 weapons- the projectile weapon (rocket launcher), the railgun (sniper weapon), and melee. Out of the 6 plants that players can plant on captured platforms, only the turret and the ramp are useful in most situations. This severely limits the player's playstyle and makes the overall game less interesting.
Secondly, because the three combat options are hitting a fast moving enemy with your fist while moving very fast, shooting a fast moving enemy with a projectile weapon with a tiny area of effect, or sniping a fast moving enemy without any sort of scope there will be a huge skill gap. New players will have a very hard time actually doing anything, so they won't want to stick around. The only way to get better is to practice.
This brings me to my third point; you can't practice because there is nobody to practice against. Most of the time, there are zero players on. The only time anyone is on is for the weekly dev game and the occasional password-protected tournament match.
Also, a lot of the maps aren't much fun to play. The only good maps are the ones with ball spawn areas that are much lower than the goals. Putting the ball spawn lower down makes it easily accessible from multiple routes, making it harder to camp the ball. It also makes it easier to defend because the ball carrier has to climb all the way up to the goal. On a flat map, one team gets to the ball first, camps there, and can easily hold off the other team while they send one player to zip across the map with a powerup and score instantly over and over again.
To the devs- I still think this game is very promising. If you can update it to make it more diverse and suitable for multiple playstyles and narrow the skill gap, then get it featured on the store frontpage with a sale you might be able to build a lasting player base.